Used with
permission of Maiken Naylor, University at Buffalo, Buffalo, NY, USA,
http://ublib.buffalo.edu/libraries/units/sel/exhibits/stamps
The metric system originated in France around the time of the French revolution and was officially adopted in 1795. Louis XVI authorized the formation of a commission, of which Lagrange was a member, to reform weights and measures. Based mainly on decimal units, it has been adopted as the standard system of measurement in science and commerce throughout the world, except in a handful of countries, including the United States, where it is legal and encouraged, but not mandatory. The meter is the international unit of length; the General Conference on Weights and Measures in Paris in 1875 was the occasion for the Treaty of the Metre signed by 18 nations, including the U.S. The meter was originally defined as one ten-millionth of the length of a quadrant meridian. In 1960 a wavelength of Krypton 86 radiation was used to redefine the meter; the original platinum-iridium meter is still preserved in Paris. Since 1983, it is defined as the length traveled by light in vacuum during 1/299792458 of a second. The second, another standard, is defined as the time required for 9,192631770 vibrations of a microwave emission line between the two hyperfine ground levels of the cesium 133 atom. The advantage of these standards lies in that they form a common basis for all scientific measurements, and that they are founded on immutable physical properties of the cesium atom.
Stamps observing the centenary of the Metric Treaty were issued by many countries: Sweden displays a simple tape measure; the French stamp shows not only the signatories to the Metric Treaty, but also a Kr 86 atom surrounded by the symbols of the metric units. The number 1,650763.73 between amplitude peaks refers to the wave number of the Kr radiation standard. The Swiss stamp shows a stylized platinum bar and characteristic Krypton radiation.
Many countries have used the metric system for over a hundred years; Brazil since 1862, and Mexico since 1857. Others have adopted it more recently: Japan in 1959, Korea in 1964.